Passenger Side Alternator Weirdness...

[LouhiKhar]

Hey all,

I don't think I'm retreading an existing issue, but correct me if I'm wrong...

Sorry for the novel... I have been trying to make sure I cover the "Duh" things first, and provide enough information here to be useful.

1986 M1008. The issue I'm trying to resolve right now is with the Gen 2 light. I know... But not *THAT* Gen 2 light issue... I've tried searching threads here, I've been poring over the TMs, and I haven't been able to find exactly what I'm dealing with.

The issue I started with was the Gen 2 light flashing when driving, especially with extra loads, like heat and headlights on. I followed the alternator testing threads and the TMs, and came to the conclusion I had a failing regulator. Through a series of unfortunate events, I ended up buying a Wilson 90-01-4277, basically a reman Delco 27SI with isolated ground, and installing that.

Now I have mostly the same problem... Still get some flashing of the Gen 2 light. I think it's slightly less than before, but same basic issue...

I didn't have a second set of hands originally, but after seeing the same basic issue, I got someone to help me out. What appears to be happening is that the voltage across the battery seems to decrease as RPMs increase, and I later confirmed this comparing fast idle to slow idle. At fast idle, I see ~14.8V over the second battery, and ~15V at slow idle. With someone revving the engine, I see the voltage drop to ~14.5V at times. I was thinking maybe the belt was slipping, but I don't hear any squealing and replacing the belt didn't affect the issue. I thought that the original alternator was supposed to have a 14.8V output, but I noticed the new alternator has a sticker stating a 14.92V setpoint. So maybe that's a factor too. As I understand it, the light turns when the battery voltage and setpoint are far enough apart, basically the output of a comparator. Maybe, if my memory is a correct (unlikely, but plausible) and the set point here is higher, I'm getting flashing when I wouldn't have with the original alternator... But that doesn't explain the charging voltage dropping when the engine is revved...

I have a battery tester, and both batteries pass cold cranking tests, so I don't think I have a bad battery. To double-check, I swapped the batteries, and didn't see much difference. Batteries appear to be ~2 years old, based on info on the stickers. They were installed before I bought the truck last year, so I'm not 100% sure. They appear to have been manufactured in January and February of 2022.

I checked to see if there was a larger than expected resistance between the alternator and the battery, but saw a dead short, so far as my multimeter could tell. I could try current-based test during start or something to get a better sense, as most multimeters can't reliable read below 0.3 ohms or so, but I haven't had a chance yet.

So I don't think I have bad batteries and the alternator is brand new... The wiring seems to match the wiring diagrams in the TMs...

My next thoughts were maybe the Gen 2 light relay is failing, or maybe the resistors are failing... I will note that I have noticed some odd gremlins in the electrical system. If I have high beams on for too long, my dash lights tend to go out. Turning high beams off and a little bit of time has my dash lights come back. It doesn't pop fuses, but lights simply turn off until the scenario is cleared, then they just come back...

So I'm in a weird spot... Based on the minimum 14.5V I measured, it should be (and seems to be, based on my measurements) enough to charge the second battery. So functionally, it seems to be OK. I'm simply concerned it will lead to other issues or is forewarning me of problems to come (like the resistors completely failing or something). The truck starts, drives, and seems to charge both batteries OK.

I still have plenty of things to do on the truck, and it originally felt like this one should have been an easy enough problem to solve. Gen 2 light comes on, measurements indicated alternator regulator, replace it. But that hasn't fixed the issue...

For completeness, I'll note that I did install a Fluidampr in October, but that's the only change to the engine I've made, aside from basic maintenance (oil change, new glow plugs, etc.). All lights in the dash have been replaced with LEDs, except the Gen 1 and Gen 2 lights, which have a traditional 168 and a 192 bulb in them. The truck did have a disabled waste vegetable oil system in it, which I have mostly removed, but there were some electrical changes, tying its computer into some sensors and the like. It's possible something is going on there, but it wasn't doing this when I originally bought the truck, so I'm not convinced that is part of the immediate problem.

Should I replace the Gen 2 light relay? Should I look into the resistors? I'm not entirely sure where to look next...

Any suggestions?

Thanks all for the read and any help you can offer.

 

[WWRD99]

Hey all,

I don't think I'm retreading an existing issue, but correct me if I'm wrong...

Sorry for the novel... I have been trying to make sure I cover the "Duh" things first, and provide enough information here to be useful.

1986 M1008. The issue I'm trying to resolve right now is with the Gen 2 light. I know... But not *THAT* Gen 2 light issue... I've tried searching threads here, I've been poring over the TMs, and I haven't been able to find exactly what I'm dealing with.

The issue I started with was the Gen 2 light flashing when driving, especially with extra loads, like heat and headlights on. I followed the alternator testing threads and the TMs, and came to the conclusion I had a failing regulator. Through a series of unfortunate events, I ended up buying a Wilson 90-01-4277, basically a reman Delco 27SI with isolated ground, and installing that.

Now I have mostly the same problem... Still get some flashing of the Gen 2 light. I think it's slightly less than before, but same basic issue...

I didn't have a second set of hands originally, but after seeing the same basic issue, I got someone to help me out. What appears to be happening is that the voltage across the battery seems to decrease as RPMs increase, and I later confirmed this comparing fast idle to slow idle. At fast idle, I see ~14.8V over the second battery, and ~15V at slow idle. With someone revving the engine, I see the voltage drop to ~14.5V at times. I was thinking maybe the belt was slipping, but I don't hear any squealing and replacing the belt didn't affect the issue. I thought that the original alternator was supposed to have a 14.8V output, but I noticed the new alternator has a sticker stating a 14.92V setpoint. So maybe that's a factor too. As I understand it, the light turns when the battery voltage and setpoint are far enough apart, basically the output of a comparator. Maybe, if my memory is a correct (unlikely, but plausible) and the set point here is higher, I'm getting flashing when I wouldn't have with the original alternator... But that doesn't explain the charging voltage dropping when the engine is revved...

I have a battery tester, and both batteries pass cold cranking tests, so I don't think I have a bad battery. To double-check, I swapped the batteries, and didn't see much difference. Batteries appear to be ~2 years old, based on info on the stickers. They were installed before I bought the truck last year, so I'm not 100% sure. They appear to have been manufactured in January and February of 2022.

I checked to see if there was a larger than expected resistance between the alternator and the battery, but saw a dead short, so far as my multimeter could tell. I could try current-based test during start or something to get a better sense, as most multimeters can't reliable read below 0.3 ohms or so, but I haven't had a chance yet.

So I don't think I have bad batteries and the alternator is brand new... The wiring seems to match the wiring diagrams in the TMs...

My next thoughts were maybe the Gen 2 light relay is failing, or maybe the resistors are failing... I will note that I have noticed some odd gremlins in the electrical system. If I have high beams on for too long, my dash lights tend to go out. Turning high beams off and a little bit of time has my dash lights come back. It doesn't pop fuses, but lights simply turn off until the scenario is cleared, then they just come back...

So I'm in a weird spot... Based on the minimum 14.5V I measured, it should be (and seems to be, based on my measurements) enough to charge the second battery. So functionally, it seems to be OK. I'm simply concerned it will lead to other issues or is forewarning me of problems to come (like the resistors completely failing or something). The truck starts, drives, and seems to charge both batteries OK.

I still have plenty of things to do on the truck, and it originally felt like this one should have been an easy enough problem to solve. Gen 2 light comes on, measurements indicated alternator regulator, replace it. But that hasn't fixed the issue...

For completeness, I'll note that I did install a Fluidampr in October, but that's the only change to the engine I've made, aside from basic maintenance (oil change, new glow plugs, etc.). All lights in the dash have been replaced with LEDs, except the Gen 1 and Gen 2 lights, which have a traditional 168 and a 192 bulb in them. The truck did have a diasabled waste vegetable oil system in it, which I have mostly removed, but there were some electrical changes, tying its computer into some sensors and the like. It's possible something is going on there, but it wasn't doing this when I originally bought the truck, so I'm not convinced that is part of the immediate problem.

Should I replace the Gen 2 light relay? Should I look into the resistors? I'm not entirely sure where to look next...

Any suggestions?

Thanks all for the read and any help you can offer.

There's a good bit to unpack here since I think you have more than one problem. I've had this exact issue with one of my rebuilt alternators I did myself. It would pass on the bench but flash once the alternator got some heat in it. The gen light would flash on and off after about 10 minutes or more of driving. After exhaustive testing mine was a bad rotor in the alternator...extremely difficult to find as all the other parts in mine were new and bench testing did not find a problem unless hot. I have several alternators here and swapped the rotor out of it with another and it stopped flashing. I'm not sure how you'd be able to get the parts store you got it from to test that on your end though. Would be hard to prove unless you had a good known rotor on hand to swap out. I don't think your relay is an issue since the alternator works and you'd here that clicking in the same time as the light would flash. I tried one of those as well and the diode pack under the dash..didn't fix it. I know it's a good bit of work but you could swap the alternators from one side to the other and see if the gen one light then starts flashing. Just make sure the new one is an isolated ground. The dip in voltage is probably the alternator charging up the battery from going through the starting procedure.
As far as the lights go it's sounds like the classic melted fuse box 30amp output side. The fuse will test fine but since the output side of the fuse is what melts a test light won't find that. I use a 90 degree pick and expand the contacts for both sides up and down to make total contact with the fuse in the box. I also changed the headlights to led style so it draws less amps plus you can see when you drive then.

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[LouhiKhar]

Like I said, sorry about the novel... I was trying to get as much information as might be relevant out there.

I could try to swap the alternators. The fact that I'm seeing roughly the same thing between the one that was in there originally and this new one makes that sort of unlikely. Not impossible, I get that. But the fact that the problem remained largely unchanged seems to me to make it more likely that something else is causing the problem. Probably worth trying, though, as I'm not sure what else to try at the moment... It is technically a reman, so it is possible that the rotor in this one is bad and they didn't find it in test after assembly. Something to consider... I'd have to double-check the driver side to make sure it's isolated ground. I know the new one is. First thing I checked... I'll have to keep an eye on the weather and try to find some time to do a swap... Looks like we have rain coming in for the next couple of days, which isn't very conducive to backyard mechanic-ing...

Thanks for the tip on the lights. I figure it's something like that, but it hasn't bothered me too much, so I haven't dug in hardly at all. I mentioned it mostly to make it clear that there are clearly some electrical issues in the truck, generally. I also have some LED headlights waiting to go in, but they have daytime running lights and turn signals built in, so to use them to their full potential, I need to do some wiring and I haven't gotten to it yet.

 

[WWRD99]

Like I said, sorry about the novel... I was trying to get as much information as might be relevant out there.

I could try to swap the alternators. The fact that I'm seeing roughly the same thing between the one that was in there originally and this new one makes that sort of unlikely. Not impossible, I get that. But the fact that the problem remained largely unchanged seems to me to make it more likely that something else is causing the problem. Probably worth trying, though, as I'm not sure what else to try at the moment... It is technically a reman, so it is possible that the rotor in this one is bad and they didn't find it in test after assembly. Something to consider... I'd have to double-check the driver side to make sure it's isolated ground. I know the new one is. First thing I checked... I'll have to keep an eye on the weather and try to find some time to do a swap... Looks like we have rain coming in for the next couple of days, which isn't very conducive to backyard mechanic-ing...

Thanks for the tip on the lights. I figure it's something like that, but it hasn't bothered me too much, so I haven't dug in hardly at all. I mentioned it mostly to make it clear that there are clearly some electrical issues in the truck, generally. I also have some LED headlights waiting to go in, but they have daytime running lights and turn signals built in, so to use them to their full potential, I need to do some wiring and I haven't gotten to it yet.

Hey write all you want!! It really helps so I don't have to ask questions to clarify. The drivers side is the only one that needs to be isolated so it should work fine. I have headlights that have all that in it too but didn't want to hook that up.

 

[Barrman]

14.4 volts is considered max output for an alternator. You seeing closer to 15 volts to mean means resistance somewhere or since the light flashes intermittently. Something loose somewhere.

Have you had a chance to remove, clean with sandpaper and or nail file and then re attach every single wire at the firewall Bussbars behind battery 2? Do the same to the wires on the engine wiring harness block over next to the glow plug relay. Check the entire length of the alternator 2 isolated ground wire as well.

My last guess is to make sure the bolt in the middle of the through the firewall harness to the back of the fuse panel is tight.

 

[LouhiKhar]

14.4 volts is considered max output for an alternator. You seeing closer to 15 volts to mean means resistance somewhere or since the light flashes intermittently. Something loose somewhere.

Have you had a chance to remove, clean with sandpaper and or nail file and then re attach every single wire at the firewall Bussbars behind battery 2? Do the same to the wires on the engine wiring harness block over next to the glow plug relay. Check the entire length of the alternator 2 isolated ground wire as well.

My last guess is to make sure the bolt in the middle of the through the firewall harness to the back of the fuse panel is tight.

So that might normally be true, but I've read here that the CUCV alternator tend to be a little higher. Additionally, there is a sticker on the Wilson reman I bought that specifically states the regulator setpoint is 14.92V, so I think I'm seeing values in line with the intended output of that alternator. I would expect a bit of drift considering the isolated grounding. If I get a chance, I'll see if I can get a picture of the sticker and post it here. Realistically, I think the higher output is the only reason I'm still charging that battery, at the moment... For reference, the Wilson site lists it as a direct replacement for the Delco Remy 1105500 in the TM parts list (-20P, for those keeping score). Here is the manufacturer's listing: https://www.bbb-cv.com/wilson/en/product/90-01-4277

I was originally thinking you might be on the right track with resistance somewhere, based on the fact that I see the voltage drop as the RPMs went up. Theoretically, if the alternator is trying to push more current to charge the battery, higher current over a resistance would cause a larger voltage drop. But I can't seem to find any connections between the alternator and the battery where my multimeter shows anything other than a dead short on the positive path. I don't have a milliohm meter, so I can't get any better than that at the moment.

I forgot to mention that the original alternator had a suppressor (capacitor with a small amount of resistance) between the isolated ground and the chassis connection on the outside, but it fell apart. The wire came loose from the metal body. I'm currently running without the suppressor, as there should be one internal to the alternator (there was when I took the old one apart), and it's really there for noise suppression, as far as I can tell. Probably trying to reduce noise for radio equipment. I was going to use a spare suppressor from one of the rebuild kits to replace it, but it doesn't have the same mounting holes, so it wouldn't fit. Again, another one of those details that probably doesn't affect things, but for completeness, I wanted to include.

I should also state that, while I'm an electrical engineer, analog was never my strongest suit. I largely understand academically how these systems work, but some of the finer points are new to me in practice, especially dealing with the split 12V/24V isolated ground stuff.

I'm super appreciative of the feedback so far. I at least have some ideas of what to try next. Not that the weather looks like it'll cooperate for the next few days...

 

[Tow4]

The regulator set point is 14.8. The regulator I included in my kits is a D101HD.
Click here for the data sheet.

 

[Barrman]

You didn’t mention the Double E thing earlier. That makes it easier to write you.

Have you a way to measure the ALT 2 voltage while driving? Going on the something loose theory I wonder if what is loose is a contact blade at the big plug on the rear of the gauge cluster. Or, the main fuse for the 24 volt side of the truck at the very bottom of the fuse panel.

You seem to have read the -20. You really are in the “trace circuit” part of the TM currently. Have you looked at the wiring diagram in the appendix to the -20? Following each and every wire end to end on the charging circuit page might be your only way out of this mess. Disassembling, cleaning and putting back together every connection while doing so of course.

 

[LouhiKhar]

You didn’t mention the Double E thing earlier. That makes it easier to write you.

Have you a way to measure the ALT 2 voltage while driving? Going on the something loose theory I wonder if what is loose is a contact blade at the big plug on the rear of the gauge cluster. Or, the main fuse for the 24 volt side of the truck at the very bottom of the fuse panel.

You seem to have read the -20. You really are in the “trace circuit” part of the TM currently. Have you looked at the wiring diagram in the appendix to the -20? Following each and every wire end to end on the charging circuit page might be your only way out of this mess. Disassembling, cleaning and putting back together every connection while doing so of course.

I did buy some voltage meters a bit ago (cheap Amazon buys when Christmas shopping), but haven't wired them in yet. The best I've gotten so far is someone revving while I'm measuring. Not quite the same thing... But what I saw there was a voltage drop as RPMs increased, which seems odd to me. I would have thought it was the other way. The alternators appear to be 3-phase, and the regulators seems to be more of a rectifier with a clamp as far as I can tell, so I would have thought that spinning the rotor faster would increase the frequency of each phase, and the rectifier would output a bit higher average. To me, the drooping voltage seems to be the key symptom...

I have digital copies of -10, -20/20P, and -34/34P, as well as a full set of hard copy manuals. Not to mention a Chilton manual and a How to Rebuild 6.2/6.5L Diesel written by the project head for the Detroit Diesels at the time... Can you tell I'm an engineer? I've started tracing things out, and that's part of why I'm confused. I haven't found the smoking gun yet, as everything seems "correct" per the manuals. One thought I did have is that I've mostly been focusing on the high side to the battery, but it occurred to me last night that I haven't really verified that the isolated ground is 100% correct. I'm wondering if the issue is the isolated ground connection is not right, maybe a bit of extra resistance there, which might cause the voltage at the battery to be wrong. If the battery and alternator are not referenced to the same point, that might explain why the voltage is shifting... Like maybe the fusible link for the alternator fused, so it's ground point is through one of the other circuits, not direct... I think that might be my next investigation, then maybe swapping alternators...

Alternatively, Tow4 confirmed a 14.8V setpoint on the regulator. If the reman I bought is really at 14.92V or whatever, could I simply be dealing with the comparator in the regulator flagging because it's expected 0.1V higher than the system does?

 

[antennaclimber]

I think your alternator may have an internal issue, or, the wire on the Number 1 terminal between the alternator and the bulb may have an intermittent ground connection. Check the wire on the #1 terminal from the alternator all the way to the GEN 2 relay to ensure that it is not connected to or touching ground somewhere.




Looking at the alternator schematic on Page 2 of the service manual, it appears that the only way for the light to come on is for the alternator to supply ground to the bulb thru pin #1.

27SI Service Manual

Unfortunately, I too have experienced defective items that are brand new, it's not fun especially at 300+ feet up!

 

[LouhiKhar]

I think your alternator may have an internal issue, or, the wire on the Number 1 terminal between the alternator and the bulb may have an intermittent ground connection. Check the wire on the #1 terminal from the alternator all the way to the GEN 2 relay to ensure that it is not connected to or touching ground somewhere.


View attachment 913548

Looking at the alternator schematic on Page 2 of the service manual, it appears that the only way for the light to come on is for the alternator to supply ground to the bulb thru pin #1.

27SI Service Manual

Unfortunately, I too have experienced defective items that are brand new, it's not fun especially at 300+ feet up!

I had thought about that too. When I removed the old alternator, I noticed that the contacts on the connector were kind of gross. I did try to clean out the contacts when installing the new alternator, but it's always possible I didn't do a good enough job. Definitely worth another look...

 

[WWRD99]

The curse of the black goo they stick in those connections!! I think at one point it was some kind of dielectric grease. You're right about these being 3 phase as well as there's a 3 pack diode on the rectifier. I didn't think about it until I was putting my alternator together last night but it's there. 3 coil connections with one going to a separate connection to the rectifier with the diode pack connection on each one going to the regulator. The rotor has 2 brushes on it. I haven't used a oscilloscope on them to see it but not sure I'd see each one without connecting inside. The rectifier should make them equal I assume. I think in the past when I did see it was when the diode pack was not working right and it would show separate waves or colliding ones. Someday I'd like to get the magnetic bench to test these rotors to hopefully make sure they're ok before I put one in. Tough to find though. Good luck in this rain!

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[LouhiKhar]

Yes, probably dielectric grease, but after 35+ there's plenty of "diesel schmoo" on everything too! With a healthy covering of rust on a lot of things, to boot...

3 connections on the stator to the diode pack, probably doing a simple half-wave rectification. Normally you'd have a capacitance or inductance to smooth things out to make the output DC-ish, which I think I saw in the back half. I think there is a capacitor and a wirewound inductor, then off to the regulator. The brushes on the rotor should be for the positive and reference set up the poles of the electromagnet to induce the currents in the stator. I've attached a picture of the stator and the inside of my old one, for reference.

Yeah, it's wet here, and looks like it will be until this weekend sometime... It could be worse... We usually have a at least a foot of snow by now, so I guess I shouldn't complain too much...

 

[Barrman]

Replacing the plug at the alternator is something I have done on all of my trucks. I didn’t even think about it in this thread. Sorry.

I’m going to write it again. Trace every single wire in the diagram posted above and clean every single connection.

You didn’t mention if your glow plug resistor is stock or bypassed. If bypassed and if your truck starts in the usual 1/2 second of cranking. That is all your ALT 2 and back battery have to do with running the truck. That isn’t much to recharge and no draw on that battery no matter how the glow plugs are wired once the engine is running.

 

[LouhiKhar]

Good point. Glow plugs are button push. I have not verified if the glow plug card is even still in the truck...

And yes, my plan is to continue tracing wires. And maybe replacing the alternator connector, just because. Once it stops raining...

 

[WWRD99]

Here's the pigtail if you wanted to get one. Pretty cheap but they do fit. I've used many!!

 

[LouhiKhar]

Awesome! Thank you kindly.

 

[LouhiKhar]

I haven't forgotten about this.... Between sickness in the house and weather outside, things haven't been conducive to working on the truck...

First, I mentioned that the setpoint on the reman alternator was a bit higher than the original (14.92 V vs 14.8 V). Finally took a picture (see attached).


I still have some wire-chasing to do, and I also wanted to see if I could directly connect the negative of the alternator to the negative of the 2nd battery, bypassing the wiring harness, to see if the behavior changes. If it does, then I definitely have a wiring harness issue...

Unfortunately, I spent today fighting with the hydraulic system instead. When I brake, the power steering effectively goes away. It fought this when I first got the truck, so I replaced basically the whole hydraulic system (pump, hydroboost, lines, etc.) with the exception of the steering box. Things were great for 8-9 months, but the problem has come back. It seemed like I was low on fluid, so I topped it up, bled the system, etc. But it doesn't seem to have helped... What concerns me is that I can hear a sound similar to air escaping in the vicinity of the hydroboost when I apply the brakes, so I'm thinking maybe the accumulator went, or a seal, or something...

The saga continues...

 

[WWRD99]

I'd test the 2 wire plug at the field before I'd jump wires to the battery. See what's there. That power steering is odd. Sounds like the hydro boost is bleeding off all the pressure. You put a filter on the return when you replaced everything? Could have some dirt in the check valve. I'd pop dexron 3 in it and see if it cleans it out.

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[LouhiKhar]

Yeah, I was going to replace the connector too, just in case.

As for the hydraulics, I just replaced what was in the truck. I didn't add anything else. I don't see a filter in the TMs, so it hadn't occurred to me.

Are you suggested trying to pull out as much power steering fluid as I can, and try dextron in it? It can't hurt, I guess. If the boost has gone bad, I can't really make it any worse...